Let $m\angle C$ be the unknown. Write an equation that adds $m\angle A$, $m\angle B$, and $m\angle C$ and sets this sum equal to the total from the previous hint.

After substituting $50^\circ$ and $60^\circ$ for $m\angle A$ and $m\angle B$, combine like terms and isolate $m\angle C$ by subtracting from $180^\circ$.

In the Desmos calculator, type 180 - 50 - 60 and press Enter. The output is the measure of angle $C$; match that value to the closest answer choice.

For every triangle, the measures of the three interior angles always add up to $180^\circ$. For $\triangle ABC$, this means:

You are given $m\angle A = 50^\circ$ and $m\angle B = 60^\circ$. Substitute these values into the equation:

Combine the known angles:

Isolate $m\angle C$ by subtracting $110^\circ$ from both sides:

So the measure of angle $C$ is $70^\circ$, which corresponds to choice C.